[Doctor john]

I replaced the convertible top switch in my 1967 LeMans, but I cannot get the nut that secures the switch tight. It threads on the bare switch and also on the installed switch without the chrome "up" "down" trimplste, but with the trim plate on there are barely enough threads for the nut to grab. The new switch is identical in size to the old one, same thread length. Any tips on installing? What size is the nut? 3/8 is the size but neither 16 nor 24 threads per inch will screw on